1. Field of the Invention
The present invention relates to an electroacoustic transducer which generates a sound by means of electromagnetic acoustic conversion.
2. Description of the Related Art
An electroacoustic transducer has a magnetic circuit in which a magnetic field generated by a magnet passes through a base member, a magnetic core and a diaphragm and returns to the magnet again. When an electric oscillating signal is supplied to a coil wound around the magnetic core, an oscillating magnetic field generated by the coil is superimposed on the magnetostatic field of the magnetic circuit so that oscillation generated in the diaphragm is transmitted to air. Thus, sound is generated.
The electroacoustic transducer is provided with terminals for supplying a current to the coil, and the terminals are often connected to a wiring pattern of a circuit board by soldering or the like in the same manner as other electronic parts.
Conventionally, when coil terminal treatment is carried out for connecting a coil wire to terminals, the coil wire is led to the outside, and connected to the terminals provided on the external surface side of a base member. Further, a potting agent such as epoxy resin or the like is applied to the external surface side of the base member so as to protect the oil connection portions and seal the housing of the electroacoustic transducer.
A coil wire is extremely thin to be easily cut off if stress is imposed on the coil wire when the electroacoustic transducer is assembled or when it is mounted on an electronic apparatus. Thus, the reliability of the parts is degraded. It has been proved that if the potting agent comes in contact with the coil wire in the process of coil terminal treatment, the number of broken coil wires increases suddenly with the increase in the number of repeated thermal shocks in a thermal shock test in which the thermal shocks are repeated at fixed time intervals between a high temperature state and a low temperature state. It is considered that the coil wires are broken because an excessive load is applied to the coil wire due to the difference in the coefficient of thermal expansion between the potting agent and the coil wire. That is, in such a structure, it is difficult to enhance the durability of the coil wire in the terminal shock test.
In addition, since current-supplying terminals are exposed to the outside, there are many opportunities to impose stress on the terminals due to physical contact, soldering, and so on. Thus, the coil wire is apt to be broken due to excessive stress imposed on the terminals.
It is an object of the present invention to provide an electroacoustic transducer of high reliability in which stress imposed on a coil wire can be reduced.
According to the present invention, there is provided an electroacoustic transducer comprising: a base member made of magnetic material; a magnetic core made of magnetic material and provided erectly on the base member; a diaphragm made of magnetic material and supported with a gap between the diaphragm and a forward end of the magnetic core; a magnet constituting a magnetic circuit together with the base member, the magnetic core and the diaphragm so as to provide a magnetostatic field; a coil disposed around the magnetic core for applying an oscillating magnetic field to the magnetic circuit; a coil bobbin interposed between the magnetic core and the coil for holding the coil; a housing member for receiving the base member, the magnetic core, the diaphragm, the magnet, the coil and the coil bobbin; a filler applied on an external surface side of the base member; and terminals for supplying an electric current from the outside; wherein each of the terminals has a protrusion portion protruding into an internal surface side of the base member, and an end of the coil is connected to the protrusion portion.
According to the present invention, protrusion portions are provided in the terminals so as to protrude into the internal surface side of the base member. The coil wire, the end of the coil is connected to the protrusion portions, and a filler such as a potting agent is applied to the external surface side of the base member. Thus, the coil wire is prevented from being in contact with the filler so that it is possible to eliminate the stress imposed on the coil wire in a thermal shock test or the like.
In addition, even if stress is imposed on the external exposed portions of the terminals due to physical contact, soldering, or the like, it becomes difficult to transmit the stress from the external exposed portions to the protrusion portions. It is therefore possible to reduce the stress imposed on the coil wire. In addition, a connection treatment portion is received inside the transducer so as to be prevented from being exposed to the outside. It is therefore possible to improve the reliability of the terminal connection portion.
Further, according to the present invention, preferably, the protrusion portions protrude in a coil axial direction.
According to the present invention, the protrusion portions are made to protrude in the coil axial direction. Thus, the axis of rotation with which the coil wire is wound around the coil bobbin becomes parallel with the axis of rotation with which the coil wire is wound around each of the protrusion portions. By use of a coil winder, the coil wire is first wound around one protrusion portion, second around the coil bobbin, and third around the other protrusion portion. Through such a step, coil winding and coil terminal treatment can be carried out by a series of procedures. It is therefore possible to simplify the manufacturing process and to reduce the cost.
According to the present invention, preferably, the coil bobbin is molded integrally with the base member.
According to the present invention, the coil bobbin is molded integrally with the base member by insert molding or the like. Thus, it is not necessary to bond the coil bobbin. It is therefore possible to improve the fixation strength of the coil bobbin to the base member, and it is possible to simplify the manufacturing process and to reduce the cost.